1. Field of the Invention
The present invention relates to a method of manufacturing an electronic device having a chip and/or an antenna, such as a contactless or hybrid or label chip card, of a type in which the electronic device includes at least one decorative sheet having a visible outer face, and at least one interface comprising an antenna.
2. Background of the Invention
A chip card or xe2x80x9csmart cardxe2x80x9d generally comprises: firstly a chip or chip module which is contained at least in part in an insulating substrate, e.g. a layer of thermoplastic material, and which is connected to a planar antenna constituting an interface; and secondly two decorative outer sheets which are made of a thermoplastic material and are disposed on either face of the chip card, and which can bear inscriptions or logos. Where applicable, a protective film or xe2x80x9coverlayxe2x80x9d, such as a varnish, covers the outer sheets.
Currently, the antennas used for contactless cards are of different types. A first type of such an antenna is formed on a specific intermediate backing sheet by copper etching using the printed circuit technique. It is then inserted between a protective outer sheet and the chip or module. The chip card is generally obtained by rolling or injection-molding during which the various sheets of thermoplastic material are bonded together and/or to the substrate.
Such an intermediate antenna backing sheet generates an extra thickness of about 130 microns, which makes it difficult to comply with the maximum thickness of 840 microns set by the relevant ISO Standard.
In addition, forming the antenna on the intermediate backing sheet constitutes an additional manufacturing step, which increases the manufacturing cost from the point of view both of materials and of time. Furthermore etching the antenna remains quite a costly operation.
A second type of such an antenna is constituted by a copper winding in air, the ends of the winding being connected to a chip or a module. The winding-and-module or winding-and-chip assembly is referred to as a xe2x80x9ctransponderxe2x80x9d.
In order to manufacture the card, the transponder is inserted between at least two thermoplastic sheets, or between two thermoplastic sheets and then embedded in an adhesive, and the resulting assembly is then rolled for laminating purposes. The difficulty of using such transponders for manufacturing cards of the xe2x80x9ccontactlessxe2x80x9d type arises from the handling problems encountered in picking up the transponders and depositing them accurately on the sheets of plastic. That problem lengthens the manufacturing cycle times.
The problem that lies behind the invention is to provide a contactless or hybrid chip card that is lower in cost while also offering good performance.
Among the antenna-forming techniques that are lower in cost, screen-printing using conductive ink is also known. Unfortunately, that technique is ill-suited for the field of chip cards, in particular contactless chip cards. Ink-drying and undulation problems arise.
The available inks dry at about 150xc2x0 C., which is incompatible with the materials commonly used in the field of chip cards, such as PVC and ABS which have softening temperatures of about 60xc2x0 C.
Other materials, such as PC and PET have higher softening temperatures, in the range approximately 120xc2x0 C. to 130xc2x0 C., that are still lower than the optimum drying temperature of such inks. However, those materials are more costly than PVC and ABS.
Screen printing on thin films or sheets of thickness less than about 600 xcexcm and on the materials of chip cards also poses problems of surface undulation that is visible to the naked eye. Such undulations can be seen on the back of such a sheet, under the turns, and they constitute an appearance defect.
In addition, in order to make high-performance antennas, it is necessary to have the best possible conductivity that can be obtained, in particular by using wider turns and provided that good drying is achieved. The problem is that the area available for an antenna is limited because of the presence of an area reserved for embossing.
Furthermore, once such inks have dried, they do not all have sufficient bending strength compatible with the standards applicable to chip cards.
Because of the above-mentioned difficulties, the trend is not to use screen printing in the field of chip cards, in particular for forming conductor circuits having good conductivity on thin films, such as high-performance antennas.
An object of the invention is therefore to mitigate the above-mentioned drawbacks in order to make a chip and/or antenna electronic device that is low in cost.
To this end, the present invention provides a method of manufacturing an electronic device having a chip and/or an antenna, such as a contactless or hybrid or label chip card, said electronic device including at least one decorative sheet having an apparent outer face, and at least one interface including an antenna. The method includes a step in which the antenna is formed on that face of the decorative sheet which is opposite its visible outer face by screen-printing using a conductive ink.
This makes it possible to simplify the manufacturing cycle, thereby reducing the manufacturing cost significantly. In addition, by means of the invention, it is possible to omit the intermediate backing sheet, thereby making it possible to reduce the thickness of the card significantly, and/or to reserve space for accommodating chips or modules of larger thickness.
According to another characteristic of the invention, the sheet is provided with pre-printed graphics and/or with a transparent protective film on its apparent outer face.
This makes it possible to simplify the printing operation because it is performed on the protective sheet and not on the chip card assembly, thereby avoiding high cost due to printing rejects.
According to another characteristic, in order to form the antenna on the decorative sheet, the method includes the following steps:
a fine backing sheet is provided that is made of a material having a softening or degradation temperature that is lower than an optimum ink-drying temperature;
a conductive ink is provided that has a metal particle content lying in the range of approximately 60% to 95% in a polymer matrix and a solvent, said ink further having a predetermined optimum drying temperature; and
after screen-printing said ink onto said backing sheet, the ink is dried partially at a temperature lower than the optimum drying temperature of the ink. The ink includes silver particles at a content lying in the range of 70% to 85%.
It is thus possible to obtain an antenna having acceptable performance by screen printing on materials used in the field of chip cards without them being degraded by the drying step.
According to another characteristic of the invention, a plurality of antennas are formed simultaneously on a decorative base sheet. The base sheet is then cut up to obtain a plurality of decorative sheets with their antennas. It is then possible to assemble the chip card. Manufacturing a plurality of protective sheets simultaneously makes it possible to obtain further reductions in manufacturing time and cost.
Advantageously, the table of the screen-printing machine is subjected to surface-smoothing treatment, such as anodization or coating with Teflon. This makes it possible to prevent scratches from forming on the printed face of the protective sheet.
According to yet another characteristic of the invention, the screen-printed sheet is dried in an oven, thereby making it possible to remove the solvent and to obtain a solid conductor tape made up of conductive particles and of a binder. Advantageously, a protective plate is simultaneously inserted between the meshed mat of the drying oven and the screen-printed sheet. This makes it possible to isolate the outer face of the protective sheet and to protect it from scratches or the like.
To this end, it is also possible to use a meshed mat that is made of a plastic material, a treated meshed mat, e.g. made of stainless steel, or else belts of plastic tape.
The invention also provides an electronic device having a chip and/or an antenna, such as a contactless or hybrid or label chip card, which device is obtained by implementing the method of the invention. It is distinguished in that it includes an antenna formed by screen-printing on the non-visible back of a decorative sheet.
According to one characteristic, the antenna includes turns of unequal widths between its connection ends. This makes it possible to increase the conductivity of a conductive ink or to compensate for its insufficient conductivity without giving rise to additional drawbacks, in particular due to drying.